Browsing by Author "Huang, Shih-Yu"

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Cathodic plasma-induced syntheses of graphene nanosheet/MnO2/WO3 architectures and their use in supercapacitors
(2020-05-10)
Huang, Shih-Yu
;
Phuoc-Anh Le
;
Yen, Po-Jen
;
Lu, Yi-Chun
;
Sahoo, Sumanta Kumar
In this study, we synthesized new 0.01-2 mu m graphene nanosheet/MnO2WO3(G/MnO2/WO3) architectures through an electrochemically induced cathodic plasma process in a single batch at a lower temperature (70 degrees C) and for a shorter time (2 h) than those required for the syntheses of similar structures when using a hydrothermal method. We first obtained 0.01-1 mu m leaf-like graphene (G) nanosheets, then 0.1-0.3 mu m long and approximately 10 nm diameter petiole-like MnO2 nanowires on the G nanosheets, and finally 0.20-2.0 mu m petal-like WO3 on MnO2/G - thereby forming the G/MnO2/WO3 architectures - as evidenced using scanning electron microscopy and transmission electron microscopy. We deciphered the step-wise reaction mechanism behind the formation of the G/MnO2/WO3 architectures during the plasma process. The high surface area of 291 m(2) g(-1) in the G/MnO2/WO3 architecture was contributed mainly by the G nanosheets, providing a suitable surface area for diffusion of the charge carriers during the charging and discharging process. As a result, an electrode incorporating the G/MnO2/WO3 architectures exhibited an excellent specific capacitance of 620 F g(-1) - 45 and 200% higher than those of G/MnO2 (421 F g(-1)) and G (189 F g(-1)) electrodes, respectively - at a current density of 0.5 A g(-1). Moreover, the G/MnO2/WO3-incorporated electrode exhibited good electrochemical cycling stability, with 90% capacitance retention over 5000 cycles at 1 A g(-1). Such new G/MnO2/WO3 heterojunction structures, not only provide high-performance electrode applications, but also suggest a potential approach toward fabricating other heterojunction structures having high surface areas for energy storage applications. (C) 2020 Elsevier Ltd. All rights reserved.
Using Different Ions to Tune Graphene Stack Structures from Sheet- to Onion-Like During Plasma Exfoliation, with Supercapacitor Applications
(2019-04-23)
Yen, Po-Jen
;
Sahoo, Sumanta Kumar
;
Chiang, Ya-Chi
;
Huang, Shih-Yu
;
Wu, Chia-Wei
In this article, we report a facile and simple approach for tuning graphene nanosheet structures (GNS) with different ions in the electrolytes through cathodic plasma exfoliation process in electrochemical reactions. We obtained sheet- and onion-like GNS when aqueous electrolyte NaOH and H2SO4, respectively, were present during plasma exfoliation in the electrochemical reactions, as evidenced from scanning electron microscopy and transmission electron microscopy images. Moreover, the onion-like GNS exhibited a specific surface area of 464m(2) g(-1) and a supercapacitive performance of 67.1F g(-1), measured at a scan rate of 5mV s(-1) in 1M NaCl; these values were much higher than those (72m(2) g(-1) and 21.6F g(-1), respectively) of the sheet-like GNS. This new approach for efficiently generating tunable stacked graphene structures with different ions, in the cathodic plasma exfoliation process, has promising potentials for use in energy storage devices.
Verifiable Visual Cryptography
(2012)
Hsu, Shuo-Fang
;
Chang, Yu-Jie
;
Wang, Ran-Zan
;
Lee, Yeuan-Kuen
;
Huang, Shih-Yu
The paper presents a verifiable visual cryptography (VC) scheme for checking the validness to the shares engaged in a VC decoding instance. The idea is to stamp a continuous pattern on the shares belonging to the same secret image, and a part of the pattern can be revealed through aligning and stacking half of two shares together. The visual coherent among the revealed patterns of all pair of shares provides evidence to the genuine of the shares engaged in the decoding process. Compare to the reported cheating prevention VC schemes, the proposed scheme maintains the original pixel expansion in VC scheme without cheating prevention ability, and the share verification process is done without resorting to any additional verification image. Besides, the proposed verification mechanism can easily be attached to any VC schemes in the literature to endow legitimate user with the ability to prevent cheating from malicious participants.